Method and apparatus for duct sealing using a clog-resistant insertable injector

ABSTRACT

A clog-resistant injector spray nozzle allows relatively unobtrusive insertion through a small access aperture into existing ductwork in occupied buildings for atomized particulate sealing of a ductwork. The spray nozzle comprises an easily cleaned and easily replaced straight liquid tube whose liquid contents are principally propelled by a heated propellant gas, such as heated air. Heat transfer is minimized from the heated propellant gas to the liquid tube until they both exit the injector, thereby greatly reducing the likelihood of nozzle clogging. A method of duct sealing using particles driven by heated propellant gas is described, whereby duct-sealing operations become both faster, and commercially practicable in inhabited commercial and residential buildings.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional patent applicationSer. No. 60/338,562 filed Dec. 3, 2001, entitled “Compactaerosol-sealant injector system,” hereby incorporated by reference.

STATEMENT REGARDING FEDERAL FUNDING

This invention was made with U.S. Government support under ContractNumber DE-AC03-76SF00098 between the U.S. Department of Energy and TheRegents of the University of California for the management and operationof the Lawrence Berkeley National Laboratory. The U.S. Government hascertain rights in this invention.

REFERENCE TO A COMPUTER PROGRAM

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains generally to atomization and drying ofliquids, particularly liquids that have a propensity to clog atomizationdevices, examples include, but are not limited to adhesives, sealants,coatings, and paint. The present invention pertains particularly todevices and methods used in the remote sealing of ducts, moreparticularly to the remote sealing of ducts used in heating,ventilation, and air conditioning (HVAC) systems, and yet moreparticularly to duct sealing systems using sealants propelled by heatedgas.

2. Description of the Relevant Art

U.S. Pat. No. 5,522,930 (the '930 patent), incorporated herein byreference, discloses a method and device for sealing leaks remotely bymeans of injecting a previously prepared aerosol into a duct system tobe sealed. However, the system uses an external heating source fordrying of the diluted aerosols that are sprayed, nominally at roomtemperature. The aerosols are diluted to reduce particle size by meansof evaporation, and thereby improve penetration of the duct system.

U.S. Pat. No. 5,980,984 (the '984 patent), incorporated herein byreference, discloses a method and device for remotely sealing ducts bycalculating the particle sizes, and injecting them into a pressurizedduct having unsealed leaks. The method of particle size calculationproduces particles that have an optimized sealing ability, yet due totheir optimized size are best transported by the bulk flow to the siteof unsealed leaks. After properly configuring a duct system as outlinedin the '984 patent, by determining the change of the duct pressure andflow during the sealing process it can be determined whether the ducthas been sufficiently sealed.

Prior nozzles tested for use in duct sealing operations have includedthose manufactured by Delavan Spray Technologies, Bete: Industrial SprayNozzles, PNR America, Schlick-Düsen, and Spraying Systems Co., as wellas various counter-rotating vortex nozzles. These prior nozzlesvariously suffered from frequent clogging and/or a particulate spraycone angle too wide for direct injection within narrow ducts.

Narrow ducts form a limiting application for duct sealing applications.In residential homes, and small ducts in commercial systems, ducts maybe as narrow as 100 cm. The narrow ducts set a limit to how wide of aspray cone angle may be for these applications. Spray cone angle is morefully developed and described in Atomization and Sprays, by Arthur H.Lefebvre, Hemisphere Publishing Company, 1978, pages 296–301, and arehereby particularly incorporated by reference. The concept relates tothe conic shape of spray as it leaves a nozzle, and is typicallymeasured photographically by viewing the included angle of the spray.For most commercial and residential duct sealing applications, the spraycone angle is preferably less than 20°, more preferably less than 15°,and most preferably less than 10°. While these spray angles work well innarrow ducts, they will also work well in wider ducts.

Counter-rotating vortex nozzles do not appear to have serious cloggingproblems, however they create large spray angles and requireconsiderable dilution (e.g. nine parts liquid to one part solid) to makeparticles in a size range suitable for sealing ducts. Such large spraycone angles are unusable for sealing narrow ducts, as a large fractionof the overall spray output is immediately coated on the sides of thenarrow duct, thereby reducing the availability of downstream sealantparticles and thereby increasing sealing time.

Compressed-air nozzles use a propellant gas (typically air, althoughother gasses may be used), and a liquid feed to create smaller liquidparticles, thereby reducing the amount of dilution required to createcorrectly sized smaller particles. The smaller particles also reduce thequantity of heat required to evaporate the diluent. By concentrating theheat in the propellant gas, heat is delivered more efficiently to theparticles, further reducing heating requirements.

When the propellant gas is heated, preferably forming simple heatedcompressed air, clogging within the atomizer is increased. The presentdevice includes the advantages of heated propellant gas, howevermitigates heat-induced clogging by limiting heat transfer to the liquidto be atomized while the liquid is resident within the device.

Both the '930 and '984 patents teach the heating of the bulk gas flowinto and through the duct. This heating serves the principal purpose ofdrying a volatile diluent added to a liquid sealant used for ductsealing. The diluent reduces the size of the sprayed sealant particlesthat remain after drying or desolvation, thereby producing theappropriate particle sizes required to penetrate and seal duct systems.

Diluting the sealant poses two problems. First, for the sealant to workeffectively, the diluent (otherwise referred to as a solvent) must beevaporated so that the particles produced consist essentially ofdesolvated sealant material. Thus, dilution increases the heatrequirements per unit mass of desolvated sealant delivered. This is animportant reason for heating the bulk flow gas into and through theduct. Significant electrical power may be required for heating the bulkflow gas depending on the size (volume of the ductwork) and leakagelevel of the ductwork being sealed, as well as the temperature andhumidity of the ambient air being used for sealing. The heated bulk gasflow rate (and thus the heating requirement) is higher for longer (hencehigher volume) or leakier ducts, and the heating requirement is alsohigher for high-humidity or low-temperature ambient air. Second, for agiven liquid flow rate, the quantity of desolvated sealant delivered tothe ducts is proportionately reduced by the amount of dilution. Forcommon dilutions of one part sealant to nine parts diluent (a ratio of1:9), sealing can take three times longer as compared to when one partsealant to three parts diluent (a ratio of 1:3) is sprayed, with otherfactors held constant. More simply stated, for the same liquid flowrate, the sealant mass flow rate is reduced by a factor of three due tothe three times higher dilution. The injector and method of using theinjector described here reduces the required sealant dilution, andthereby increases the sealant mass flow rate.

Another disadvantage found in current embodiments of both the '930 and'984 patents is the requirement that the ducts be connected to anexternal fan and spray apparatus, which may be difficult to install, andintrusive in inhabited buildings. In these situations, considerable timeand expense may be required simply to gain access to the ducts andisolate the HVAC equipment from the aerosol particles.

The above disadvantages and more are addressed in the present apparatusand method of using the apparatus, yielding a much less intrusive systemcapable of in-situ duct sealing of previously installed duct systems inoccupied commercial and residential buildings. By occupied, we refer tobuildings tenanted and in normal use. For previously installed HVACsystems capable of creating sufficient gage air pressure (known in fluidmechanics as “pressure head”, or more simply “head”), no external fanassistance is required to increase the head. This situation isfrequently found in commercial structures that have higher-pressure fansystems, and more recently in residential high-pressure HVAC systems. Inmost homes, there is insufficient head produced to allow effective ductsealing, and an additional fan must be placed in series with, and inaddition to, the originally installed fan in order to raise the headsufficiently to seal the ducts. The additional series fan createssufficient additional differential pressure in the duct system to forcesealant particles through existing duct leaks; the particles, in turn,seal the duct leaks. After sealing has been accomplished, the series fanis removed, leaving the original fan system intact. The current injectorallows the sealant spray to be created internally within the ductsystem, thereby simplifying the connection of the external fan to theduct system and the isolation of the HVAC equipment from aerosolparticles. Nearly all fan systems have doors for fan access, however theatomizers used by the earlier inventions for duct sealing applicationsdid not allow use of those access doors to connect the external fan, asthe aerosol particles were created right at the external fan, and wouldbe blown through the fan and HVAC equipment, thereby unacceptablycoating the equipment with sealant. The current injector allows thesealant spray and the external fan to be separated.

The present injector allows for easily patched access to architecturallycovered ductwork, allowing for easy placement of compact injectorsthroughout the building duct system.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a first aerosol injector is disclosed, the injectorcomprising: a liquid tube, with a liquid tube orifice for ejecting aliquid to be atomized; a propellant cap comprising: an annular orifice,the annular orifice disposed around an inner cylinder, the innercylinder passing through the propellant cap, the inner cylinder havingan interior, the liquid tube disposed within the inner cylinderinterior; an interior region flowing to the annular orifice; a gas lineflowing a pressurized gas into the interior region, the gas line havinga gas line heater, the gas line heater heating the pressurized gas toform a heated pressurized gas; a heat transfer region disposed betweenthe inner cylinder and the liquid tube; where the heated pressurized gasis ejected from the annular orifice surrounding the liquid ejected fromthe liquid tube orifice, atomizing and heating the liquid.

In another embodiment of the first aerosol injector the heat transferregion is comprised of one or more materials with a thermal conductivityof preferably less than or equal to

${25\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}},$more preferably less than or equal to

${20\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}},$yet more preferably less than or equal to

${15\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}},$still more preferably less than

${10\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}},$and most preferably less than

$5{\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}.}$

In another embodiment of the first aerosol injector the heat transferregion is comprised of one or more materials selected from the groupconsisting of: essentially stagnant air, epoxy, plastic, stainlesssteel, glass fibers, fluorocarbons and glass. The heat transfer regionis designed to limit heat transfer from the heated pressurized gas tothe liquid to be atomized.

For each fluid, there is a potentially complex relationship between thefluid temperature distribution, mass flow rate, and time required forclogging. This is easiest to comprehend with epoxies, which have atime-temperature curing rate described by the Arrhenius equation κ=Ae^(−B/T), where κ is the rate constant of a reaction, T is thetemperature in degrees Kelvin, and A and B are constants in a specificchemical system. In the Arrhenius equation, increasing temperatureproduces an increase in the reaction rate. In practical terms, if therate is sufficiently increased so as to crosslink enough bonds in anepoxy resin, then the material hardens, causing clogging. In othersuspended particulate liquids, a similar rate-temperature relationshiplikely exists, implying that increased temperatures imply increasedclogging. When clogging occurs for a particular device at particularoperating conditions, the liquid flow has reached a criticaltemperature. Keeping the liquid below this temperature precludes, orsubstantially reduces, clogging of the liquid.

In another embodiment of the first aerosol injector the liquid to besprayed is selected from the group comprising sealant, adhesive,coating, and paint.

In another embodiment of the first aerosol injector the liquid tube hasan essentially constant cross-sectional area in the heat transferregion. Although the term “tube” typically connotes a cylindrical shape,other closed conic sections or polyhedral shapes having essentiallyconstant cross-sectional area in the heat transfer region could be used.

In another embodiment of the first aerosol injector the heat transferregion contains an ambient airflow; the ambient airflow is drawn by theheated pressurized gas exiting the annular orifice; whereby the ambientairflow cools the liquid tube, and prevents boiling of the liquid.Alternatively, the ambient airflow cools the liquid tube to sufficientlyreduce heat transfer to keep the liquid below its critical temperaturein the particular system.

In another embodiment of the first aerosol injector, a method of sealinga previously installed duct using the first aerosol injector isdisclosed, the sealing method comprising: forming a duct access regionthrough one side of a previously installed air duct, the air duct havingan air flow with an air flow direction; inserting the aerosol injectorinto the previously installed air duct through the access region;aligning the aerosol injector with the direction of air flow in theduct; activating an air flow within the duct; and spraying a sealantthrough the aerosol injector to seal the duct in the direction of theair flow.

In another embodiment of the first aerosol injector, the aerosolinjector produces an aerosol spray cone angle of preferably less than20°, more preferably less than 15°, and most preferably less than 10°.The spray cone angle is ultimately controlled by varying the momentumdistributions of the liquid and heated pressurized gas. When bothmomentum distributions are most closely aligned with the central axis ofthe liquid tube, the resultant spray cone angle will be narrowest.Conversely, if the heated pressurized gas has a momentum distributionsignificantly diverging from the central axis of the liquid tube, thespray cone angle will be much wider. The momentum distributions are bestcontrolled by having aligned orifices having a characteristic lengthpreferably five times or greater than the hydraulic depth of the flow,more preferably ten times, and most preferably 20 times. In suchsystems, divergent bulk momentum is collimated into the bulk flowmomentum vector, as exemplified by pressurized water exiting a longpipe.

A method of sealing a previously installed duct is disclosed using thefirst aerosol injector, the method comprising: forming a duct accessregion through one side of a previously installed air duct; inserting aninjector into the previously installed air duct through the accessregion; the injector with the longer direction of the duct; an air flowwithin the duct; and spraying a sealant through the injector to seal theduct in the direction of the air flow. In order to form the duct accessregion, it may first be necessary to make an access opening (usually,but not necessarily a hole) in a wall, floor, or ceiling.

In another embodiment of the aerosol injector, a second aerosol injectorcomprises: a liquid tube, with a liquid tube orifice for spraying aliquid; a gas cap comprising: gas nozzle, the gas nozzle having an opencylindrical wall, forming an outer diameter of an annular tube, a gasline feeding into the gas nozzle, a gas line heater for heating apressurized gas in the gas line, forming a heated pressurized gas, aventuri bore disposed within the gas nozzle and passing through the gasnozzle, the venturi bore forming an inner diameter of the annularorifice; liquid tube passing through the venturi bore; a venturi regiondisposed between the inner diameter of the annular orifice and theliquid tube; where the pressurized gas introduced into the gas line isheated by the gas line heater, and exits the annular orifice as theheated pressurized gas, drawing ambient air through the venturi region,thereby forming a venturi flow; whereby the venturi flow cools both theinner annulus and the liquid tube, and thereby reduces heat transferfrom the heated pressurized gas to the liquid tube.

In yet another embodiment of the aerosol injector, a third aerosolinjector comprises: a liquid tube, with a liquid tube orifice forejecting a liquid to be atomized; a gas cap comprising: annular orificehaving an inner diameter, the annular orifice disposed around the liquidtube, the liquid tube having a portion disposed within the gas cap, theliquid tube forming the inner diameter of the annular orifice, theliquid tube having a constant cross section in the gas cap disposedportion; an interior region flowing to the annular orifice; a gas lineflowing a pressurized gas into the interior region, the gas line havinga gas line heater, the gas line heater heating the pressurized gas toform a heated pressurized gas; where the heated pressurized gas isejected from the annular orifice surrounding the liquid ejected from theliquid tube orifice, atomizing and heating the liquid.

In another embodiment of the third aerosol injector, the liquid tube iscomprised of one or more materials selected from the group having athermal conductivity of preferably less than or equal to

${25\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}},$more preferably less than or equal to

${20\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}},$yet more preferably less than or equal to

${15\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}},$still more preferably less than

${10\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}},$and most preferably less than

$5{\frac{W}{m\mspace{14mu}{^\circ}\mspace{20mu} K}.}$

In another embodiment of the third aerosol injector, the liquid isselected from the group comprising sealant, adhesive, coating, andpaint. Virtually any liquid having material dissolved or suspended maybe used as the liquid to be atomized.

In still another embodiment of the third aerosol injector, a method ofsealing a previously installed duct using the third aerosol injector isdisclosed, the sealing method comprising: forming a duct access regionthrough one side of a previously installed air duct, the air duct havingan air flow with an air flow direction; inserting the aerosol injectorinto the previously installed air duct through the access region;aligning the aerosol injector with the direction of air flow in theduct; activating an air flow within the duct; and spraying a sealantthrough the aerosol injector to seal the duct in the direction of theair flow. The spraying continues until sufficient pressure rise anddecrease in ductwork flow rate is detected to signal completion of theduct sealing, as described in the '984 patent.

In another embodiment of the third aerosol injector, the third aerosolinjector produces an aerosol spray cone angle of preferably less than20°, more preferably less than 15°, and most preferably less than 10°.In the most preferably injector, dried or desolvated particles arecreated in the bulk flow prior to impingement on any duct surface, andhave both bulk and small-scale eddy velocities the same as theuninjected bulk flow.

In still another embodiment of the aerosol injector, a fourth aerosolinjector comprises: a spray nozzle apparatus having a spray tip formedof co-terminal, concentric elements, comprising: an innermost liquidtube for delivering to a liquid exit tip a liquid to be sprayed; aninner hollow member surrounding said liquid tube and defining athermally insulating space between the innermost liquid tube and thehollow member; and an outermost propellant cap defining a propellantdelivery and exit space between an outer surface of the inner hollowmember and an inner surface of the propellant cap, said propellantdelivery and exit space communicating with a delivery tube for heatedpropellant gas, whereby the heated propellant gas exiting the propellantdelivery and exit space mixes with liquid exiting the liquid exit tip toform a spray.

In another embodiment of the fourth aerosol injector, the liquid exit ofthe liquid tube and the propellant exit space essentially define a planeorthogonal to the spray direction.

In another embodiment of the fourth aerosol injector, the thermallyinsulating space is occupied by air flowing into the nozzle apparatusand out of the insulating space adjacent the liquid tip exit.

In another embodiment of the fourth aerosol injector, the thermallyinsulating space is provided by a thickness of the innermost liquidtube, said innermost liquid tube being one or more of the groupcomprising epoxy, plastic, stainless steel, glass fibers, fluorocarbonsand glass.

In another embodiment, the present injector may be further characterizedas comprising a spray nozzle apparatus having a spray tip formed ofco-terminal, concentric elements. That is, the elements of the nozzle,when viewed end on, are co-terminal in that they terminate inapproximately the same area, looking into the direction of spray. Thisarea may be configured to form a planar array in the various exit tipslie in essentially the same plane. This planar array may be variedsomewhat by varying the lengths of the various delivery tubes, but isadapted to provide a mixing of liquid and propellant immediatelydownstream of the exit. The planar array is orthogonal, i.e. at rightangles to, a line drawn through the center of the spray cone.

The elements are concentric in that the primary elements, liquid tube,inner hollow member and propellant cap (described below) are configuredto provide flow channels that are radially adjacent and may be viewed assymmetrical about a central axis. The elements need not be exactlysymmetrical, but may be varied according to design parameters inaccordance with the present teachings.

In another embodiment, a spray nozzle comprises: an innermost liquidtube for delivering to a liquid exit tip a liquid to be sprayed; aninner hollow member surrounding said liquid tube and defining athermally insulating space between the innermost liquid tube and thehollow member; and an outermost propellant cap defining a propellantdelivery and exit space between the inner hollow member and thepropellant cap, said propellant delivery and exit space communicatingwith a delivery tube for heated propellant gas.

The innermost liquid tube is preferably cylindrical, but other shapesmay be employed. The inner hollow member is also preferably cylindrical,and is referred to below as an “inner cylinder.” The outermostpropellant cap provides a receiving chamber for heated propellant gas.The heated propellant gas is prevented from heating the liquid by athermally insulating space, which may be flowing air or other insulatingmaterial, as described above. This thermally insulating space isalternatively known as the heat transfer region. The air flows into andout of the nozzle by a venturi effect created by the spray.

The heated propellant gas exiting the propellant delivery and exit spacemixes with liquid exiting the liquid exit tip to form a spray becausethe exit areas are located in close proximity with each other.

In one embodiment of the spray nozzle apparatus, the thermallyinsulating space is provided by a thickness of the innermost liquidtube, said innermost liquid tube being one or more of the groupcomprising epoxy, plastic, stainless steel, glass fibers, fluorocarbonsand glass. That is, the thickness of the innermost liquid tube is suchthat the liquid tube itself has insulating properties; the innermostliquid tube is adjacent to, and in contact with the propellant deliveryspace and insulates the liquid from the heated propellant gas.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be more fully understood by reference to thefollowing drawings, which are for illustrative purposes only:

FIG. 1 is a perspective view of a compact sprayer assembly placed in acut away section of duct for a duct sealing operation.

FIG. 2 is a partially cut away view of a compact sprayer assembly.

FIG. 3A is a partial cross-sectional view of the sprayer nozzle assemblywith venturi cooling limiting heat transfer.

FIG. 3B is a partial cross-sectional view of the sprayer nozzle assemblywith an insulator limiting heat transfer.

FIG. 3C is a partial cross-sectional view of the sprayer nozzle assemblywith the liquid tube partially disposed within the gas cap, and therebylimiting heat transfer.

FIG. 4 is a partial cross-sectional view of the sprayer nozzle assembly,with the various flow patterns depicted.

FIG. 5A is an exploded cross-sectional view of the sprayer nozzleassembly.

FIG. 5B is the sprayer nozzle assembly viewed on end from the directionof spray.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In general, the present compact aerosol sealant injector providesnebulization or atomization of a pressurized liquid supply at a locationnear the nozzle tip. When the liquid supply is ejected in closeproximity to the propellant, turbulent mixing occurs, forming a fineliquid mist, or liquid spray. The turbulent mixing phenomenon isextremely complex, depending on variables such as: relative flowvelocities, densities, viscosities, surface tensions, and temperaturedistributions, etc., in both flows. Further representative referencesregarding the physics and fluid dynamics of atomizers and sprayers,incorporated herein by reference, are: Atomization and Sprays, by ArthurH. Lefebvre, Hemisphere Publishing Company, 1978; and LiquidAtomization, by L. Bayvel and Z. Orzewchowski, Taylor & Francis, 1993.This phenomenon becomes yet more complex when a heated propellant gas isused to desolvate or dry particles in the liquid supply.

Heating the propellant gas has many advantages. The fine liquid mistinitially has a very high surface area to volume ratio, which leads torapid desolvation. Additionally, since the liquid mist is heated by thebulk propellant flow, solvent evaporation occurs at an even higher ratedue to the increase of the solvent vapor pressure. Nearly all solventsexhibit higher vapor pressure with temperature. Higher temperaturestypically imply decreased viscosity and surface tension, both of whichtend to induce particulate breakup into fine particles. These effectscombine to quickly reduce the liquid mist particles to a cloud ofindividual particles without significant remaining liquid diluent. Asthe diluent of the diluted sealant particles is reduced, the particlesurface area to mass ratio increases yet further, which leads to anincreased tendency for the particles to remain in suspension of the bulkduct gas. With a higher fraction of particles suspended, there is lessparticle settling, and consequently improved sealing in duct sealingapplications over longer duct distances, as previously discussed in the'984 patent.

In some sprays, dilution is unnecessary. In other sprays, a diluent maybe added to adjust the resultant desolvated sealant particle to achievea particular size. By being able to tailor the particle size, optimalsealant particle sizes may be obtained for optimal sealing.

By heating just the propellant gas, heating requirements for the bulkair flow in the duct are reduced or eliminated, and the overall heatingenergy requirements are reduced considerably, further making the sealingsystem more compact and less intrusive. Furthermore, by propelling thesealant with a heated gas stream, less solvent is needed to spray thesealant, thereby increasing the mass flow rate of the sealant, and thusthe rate of sealing.

When the inventors initially began using heated propellant gas, it wasdiscovered that the traditional spray nozzles would quickly clog,disrupting the duct sealing process. This occurred with a debilitatingfrequency to the point that a new nozzle with dramatically reducedclogging was created. This nozzle has such a great reduction in cloggingfrequency that it is referred to as the clog resistant nozzle.

Clogging in spray nozzles may typically be classified in threecategories: steady state operation clogging in continuous use, cloggingoccurring during a prolonged break period while not spraying, andcyclical clogging related to the number of intermittent sprays andbreaks. Additionally, when heating a liquid for spraying, it has beenfound that the liquid may be more prone to clogging.

Heat-induced clogging is reduced by thermally isolating the heatedpropellant gas from the liquid to be atomized until both exit thenozzle. The present injector and method of using the injector alsocombines localized direct propellant gas heating with a small spray coneangle to allow injection directly within a duct—even ducts with narrowdimensions. By using tubing for liquid injection, which is straight withconstant cross-sectional area, the present injector further reducesclogging, and increases cleaning and liquid-line replacement efficiency.Clogging due to reductions in cross-sectional area within the heatedzones is dramatically reduced. Should clogging occur in the liquid tube,a suitably sized wire readily accomplishes cleaning. Should suchcleaning become impossible, replacement of the liquid tube within theheated zone is easily accomplished given the embodiments describedbelow.

A. Clog-Resistant Compact Aerosol Sealant Injector Nozzle

The novel injector nozzle design disclosed herein addresses severalimportant issues useful for general spraying operations, and moreparticularly duct sealing operations. In both of these operations, aliquid comprising dissolved chemicals or suspended particles is sprayed.Typical liquids include but are not limited to paints, adhesives,coatings, solvents, particulate suspensions, colloidal suspensions,gasses, dissolved gasses, or other fluids, as well as combinations andmixtures of these, and particularly dilutions and solvents added tothese. For simplicity, the aforementioned liquid will interchangeably bereferred to herein as a liquid, sealant, coating, paint or adhesive.

Many of the liquids described in the paragraph above tend to clogsprayers. This clogging problem is frequently exacerbated when theliquid is heated. Inadvertent heat transfer from the propulsion gas (orpropellant gas) to the liquid to be sprayed can result in the “cooking”or “baking” of the liquid by boiling off of the liquid solvent,premature agglomeration, aggregation, or chemical reactions, all ofwhich separately or in combination tend to induce clogging by reaching acritical temperature in the liquid. Preventing this type of heat inducedclogging is achieved by minimizing heat transfer between the unheatedliquid to be sprayed and the heated propulsion gas until just outsidetheir respective spray orifices, thereby maintaining the unheated liquidbelow its critical temperature.

Special heat transfer minimization methods are used in the nozzle tolimit heat transfer from the heated propulsion gas to the liquid flowprior to liquid efflux. In one embodiment of the nozzle, the highvelocity of the heated gas efflux creates a venturi-generated lowpressure region, which is in turn used to draw ambient, non-heated air,over a tube containing the liquid to be sprayed, thus minimizing heattransfer from the heated propulsion gas to the sealant. The pressure ofthe low-pressure region may be obtained by the well-known Bernoulliequation widely used in hydraulics and fluid mechanics. The result isgreatly reduced clogging of the spray nozzle. Other embodiments employthermal insulation techniques in various configurations to minimize heattransfer.

It has been found that the liquid tube is optimally straight, and with aconstant cross section, throughout the region where any significant heattransfer is taking place, that is, the region that contains heatedpropellant in close proximity to the liquid tube. Restating this, it hasbeen found by the inventors that both changes in cross section andchanges in flow direction when heat is entering the liquid tube tend toinduce more frequent clogging. The optimal embodiment found for theliquid tube has been a straight cylindrical tube, which has bothconstant cross-section and is straight. The tube most preferably has lowthermal conductivity (e.g. stainless steel rather than brass or copper)to further minimize heat transfer.

The resultant compact injector can be packaged into a cylindrical volumesmall enough to place into holes formed through an architecturalcovering, e.g. a wall, ceiling, or even a structural member, and throughthe duct. The depth of the duct's near and far wall are then measured.The injector is then adjusted to minimize deposition near the injectionpoint, preferably a depth of 55% of the duct depth for horizontal ductsin ceilings, 45% for floors. Mid depth, or 50% insertion, is used forvertical ductwork with the flows moving either up or down. Any of theseinjector placement locations may be moved all the way to eitherinsertion extent, however, as much as 50% of the sprayed liquid is thenimmediately deposited on the proximal duct surface, resulting indecreased duct sealing rates.

The compact injector is an extremely efficient method for sealinginstalled ductwork systems, especially those found in occupied largecommercial buildings. For these large ductwork systems, several compactaerosol sealant injectors are installed directly in the ducts downstreamof sensitive ductwork components, such as fans and heat exchangers. Theinjectors may then be run either sequentially or simultaneously asrequired with existing fans alone, or with existing fans in conjunctionwith one or more differential pressure augmenting series fans.

Prior to this compact injector, commercial aerosol sealant injectionfaced several problems achieving multiple simultaneous injection ininstalled duct-work systems: 1) due to the bulky dimension of thepreviously existing compact aerosol-sealant injectors, it took too muchtime to install, remove and restore the duct system after injection; 2)prior injectors typically had wide spray cone angles, meaning that theycould not be used to inject at adequate sealant flow rates in duct withsmall cross-sectional dimensions, since the spray would principally bedeposited in the immediate vicinity of the injector; 3) prior injectorstypically created relatively large particle sizes, which meant that thesealant had to be diluted to reduce particle size, and thereforerequired significantly more electrical power per unit solid sealantmaterial produced; and 4) electrical power availability, ductdimensions, and low sealing rates limited duct sealing applications.

B. Nozzle Sprayer Assembly

Refer now to FIG. 1 depicting a compact injector duct sealing operation100. A compact injector 200 comprising a nozzle assembly 300 (describedin detail later in FIGS. 2 and 3) is inserted through a duct 110section, having a duct access opening 120. The nozzle assembly 300 isaligned in the direction of duct flow, at a vertical position ofpreferably about 40–50%, most preferably 55%, of the height “h” of theduct.

Refer now to FIG. 2. A compact injector 200 is comprised of a supportingtube 210, an alignment guide 220 surrounding the supporting tube 210 andadjustably attached thereto, with a directional indicator 230 on bothsides of the alignment guide 220 indicating the direction of spray. Theliquid to be sprayed (not shown) is pumped (also not shown) so that itenters through inlet tube 240, which ultimately connects to apressurized liquid source (also not shown). Another fluid, preferablypressurized room temperature air, enters through propellant tube 250. Acutaway section 260 appears for illustrative purposes in supporting tube210. The cutaway shows some of the propellant tube 250 shrouded withinsupporting tube 210, and an inline heater 270, which heats the contentsof the propellant tube 250 prior to efflux at the nozzle assembly 300.The contents of the propellant tube 250 is a propellant gas. Thepropellant gas is preferably heated to 50–700° C., more preferably to150–500° C., and most preferably to 300–400° C.

Refer now to FIG. 3A. The nozzle assembly 300 comprises a nozzle base305, upon which is supported a propellant cap 310 that has an opencylindrical wall 311, and an interior propellant region 320 open only inthe spray direction through the opening in the open cylindrical wall311. The propellant cap 310 also has a propellant seal piece 312 with aninner cylinder 315. The propellant seal piece 312 seals to thepropellant cap 310 except for an annular orifice 325 formed by the opencylindrical wall 311 and the inner cylinder 315. The inner cylinder 315is attached at one end to the propellant seal piece 312. In manufacture,the inner cylinder 315 is preferably formed by turning down thepropellant seal piece 312 on a lathe so that the inner cylinder 315 isintegral with the propellant seal piece 312. The inner cylinder 315additionally surrounds a liquid tube 365. Heated air initially comesfrom the propellant tube 250 (shown on FIG. 2) through the inline heater270 (also shown on FIG. 2), to the propellant cap inlet fitting 330,which positively retains the propellant cap 310 to the nozzle base 305.

Still referring to FIG. 3, a liquid cap 340 is similarly sealed with aliquid cap plug 345 to create an inner liquid region 350. The liquid cap340 is similarly positively retained to the nozzle base 305 by liquidcap inlet fitting 360, which in turn connects to the liquid inlet tube240 (shown in FIG. 2). The liquid tube 365 has an end 370 protruding alength 375 (of a predetermined distance) into the inner liquid region350. This length is designed to prevent clogging, and can range from 1to 20 liquid tube 365 outer diameters, more preferably 2 to 10diameters, and most preferably 3 to 6 diameters. Alternatively, thelength can be determined experimentally so as to reduce or eliminateclogging in the inner liquid region 350. The liquid tube 365 is sealedwith a threaded compression member 380 driving a circumferentialcompression swaging member 385 (in the art, this is typically referredto as a ferrule, but may be made of aluminum, brass, other metals, orplastics instead of ferrous materials) to seal against a male threadedextension 343 protruding from the liquid cap 340 on the side facing theannular orifice 325. The liquid tube 365 passes from the inner liquidregion 350 through the interior bore of the inner cylinder 315 of thepropellant seal piece 312 attached to the propellant cap 310, leaving anannular space sufficient to draw ambient air through a venturi entrance395 formed by the propellant seal piece 312, over the outer diameter ofthe liquid tube 365, and to the venturi exit 390.

C. Flow Paths in the Clog-Resistant Injector Nozzle

Refer now to FIG. 4. The heated propellant flow 410 passes through thepropellant cap inlet fitting 330, and flows to the propellant cap 310open interior propellant region 320. The propellant cap 310 is typicallyclose to the bulk temperature of the heated propellant flow 410. Thepropellant flow is then emitted from the annular gas orifice 325 as apropellant gas orifice efflux. Similarly, the liquid flow 420 passesthrough the liquid cap inlet fitting 360 and proceeds to the liquid cap340 inner liquid region 350. The liquid flow 420 proceeds to enter theliquid tube 365 at inlet end 370, where it traverses the liquid tube 365and ultimately exits in close proximity to the annular orifice 325, as aliquid efflux. Both the heated propellant flow 410 and the liquid flow420 are pressure driven either directly or indirectly by externalpressurization equipment such as pumps or compressed gas.

The propellant flow 410 creates a low pressure region adjacent to theannular orifice 325, which operates to draw an ambient air flow 430through a venturi entrance 395, over the outer diameter of the liquidtube 365, and to the venturi exit 390. This ambient air flow 430operates to minimize conducted and convected heat transfer from theheated propellant flow 410 (which is in contact with the outer bore ofthe inner cylinder 315), to the interior bore of the inner cylinder 315and thence to the liquid tube 365. Additionally, should any heat beradiatively transferred from the inner bore of the inner cylinder 315 tothe liquid tube 365, the continual incoming stream of ambient air flow430 acts to reduce the liquid tube 365 temperature to ambient by contactconvection. The combination of these flows tends to keep the liquid flow420 at near ambient temperatures, which operates to greatly reduce thefrequency of heat-induced liquid tube 365 clogging.

Refer now to FIGS. 3B and 4. In an alternative injector embodiment,indicated in FIG. 3B, a lamination of one or more insulation materials335 operate to minimize heat transfer from the interior bore of theinner cylinder 315 to the liquid tube 365. In a typical application, anymaterial with sufficiently low thermal conductivity may be used tothermally isolate (or effectively insulate by reducing heat transfer)the heat transfer region defined between the inner cylinder 315 and theliquid tube 365. Again, the measure of “sufficiently low” can bedetermined by the mass flow rate of the liquid flow 420, anddifferential temperatures of the liquid flow 420 and propellant flow430. Any insulator with “sufficiently low” thermal conductivity willgreatly reduce or completely eliminate clogging of the liquid flow 420by keeping the liquid below its critical temperature for clogging.

In another embodiment, an insulating material limits heat transfer.Insulators as used here are materials having a relatively low roomtemperature thermal conductivity in Watts per meter per degree Kelvin

$\left( \frac{W}{{m\mspace{11mu}}^{{^\circ}\;}\mspace{11mu} K} \right)$when compared to brass

$\left( {107\frac{W}{{m\mspace{11mu}}^{{^\circ}}\mspace{14mu} K}} \right),$copper (386), and aluminum (229). Examples of some of these insulatorsare solids such as stainless steel

$\left( {16\frac{W}{{m\mspace{11mu}}^{{^\circ}\mspace{14mu}}K}} \right),$Pyrex glass (1.09), window glass (0.78), and porcelain enamel (15.5).Other insulator examples may be cast epoxy (0.52) or plastics such asmelamine (0.48), glass filled nylon (0.5), nylon with no glass filling(0.24), polyethylene (0.33), fluorocarbons polytrifluorochloroethylene(PTFCE) (0.251), polytetrafluorethylene (PTFE) (0.24), polyvinylidenefluoride (PVF₂) (0.24), 40% glass filled polycarbonate (0.222), andstill, or stagnant air (0.026).

Many other types of plastics may be used as insulators in this injectorsubject to operating temperature limits, such as the thermoplasticresins, which include: (1) acrylonitrilebutadiene-styrene (ABS) resins;(2) acetals; (3) acrylics; (4) cellulosics; (5) chlorinated polyethers;(6) fluorocarbons, such as polytrifluorochloroethylene (PTFCE),polyvinylidene fluoride (PVF₂), polytetrafluorethylene (PTFE),polychlorotrifluoroethylene (CTEE), and fluorinated ethylene propylene(FEP); (7) nylons (polyamides); (8) polycarbonates; (9) polyethylenes(including copolymers); (10) polypropylenes (including copolymers); (11)polystyrenes; and (12) vinyls (polyvinyl chloride). Alternatively, manythermosetting resins may also be used as an insulator, including: (1)alkyds; (2) allylics; (3) the aminos (melamine and urea); (4) epoxies;(5) phenolics; (6) polyesters; (7) silicones; and (8) urethanes.

For the purposes of this injector, an effective insulator will have athermal conductivity of less than 25 Watts per meter per degree Kelvin

$\left( \frac{W}{{m\mspace{11mu}}^{{^\circ}}\mspace{14mu} K} \right),$preferably less than 20, more preferably less than 10, and mostpreferably less than

$5{\frac{W}{{m\mspace{11mu}}^{{^\circ}}\mspace{14mu} K}.}$

FIG. 3C shows yet another embodiment of the aerosol injector where amodified propellant cap 337 resembles the liquid cap 340. A propellantcap plug 335 has a central hole 336 allowing the placement of the liquidtube 365 within the central hole 336. An annular orifice 338 is formedwith the liquid tube 365 forming an inner diameter, and the central hole336 of the propellant cap plug 335 forming the outer diameter. In thisconfiguration, the relative dimensions, mass flow rates, andtemperatures are such that clogging is still reduced below a usablelevel.

This mode of operation preferably uses a stainless steel liquid tube 365acting as an insulator to reduce heat transfer. The liquid tube 365 mayalso be a laminate comprised of one or more low conductivity materials.The heat that is transferred is in turn carried away by the liquid tube365 contents before so much heat is transferred as to precipitatesubstantial clogging. In this manner, the liquid is kept below itscritical temperature.

D. Exploded View of the Clog-Resistant Injector Nozzle

Refer now to FIG. 5A, which details the individual components of theclog-resistant injector nozzle 300 as earlier depicted in FIG. 3A. Thevarious assembly lines on FIG. 5A describe how the components areassembled. Assembly proceeds with the propellant cap inlet fitting 330being inserted into the nozzle base 305. The propellant cap 310 is thenattached to the propellant cap inlet fitting 330. The propellant cap 310has previously had propellant seal piece 312 inserted. Similarly, theliquid cap inlet fitting 360 is inserted into the nozzle base 305, wherethe liquid cap 340 is attached. The liquid cap 340 has previously beensealed with the liquid cap plug 345, and has been loosely attached tothe threaded compression member 380 encapsulating and driving thecircumferential compression swaging member 385 to seal against a malethreaded extension 343 protruding from the liquid cap 340 on the sidefacing the annular orifice 325. Once the propellant cap 310 and liquidcap 340 are assembled, the liquid tube 365 is inserted through thepropellant cap 310 into the liquid cap 340, and secured by tighteningthe threaded compression member 380, which drives the circumferentialcompression swaging member 385 to seal against the liquid tube 365 andthe threaded male extension 343.

Refer now to FIG. 5B, which is viewing the assembled propellant capcomponents along the axis of the liquid tube 365. Starting at the outerperiphery of the propellant cap 310 (which is typically machined fromhexagonal brass stock), the open cylindrical wall 311 is observed. Theopen cylindrical wall 311 forms the outer diameter of the annularorifice 325, whose inner diameter is formed by the inner cylinder 315projecting off of the propellant seal piece 312 (shown in FIG. 5A). Theventuri exit 390 is another annular orifice defined by the interior ofthe inner cylinder 315, and the outer surface of the liquid tube 365.Liquid flows from the terminus of the liquid tube 365, otherwisereferred to as the liquid tube orifice.

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication or patent application were eachspecifically and individually indicated to be incorporated by reference.

The description given here, and best modes of operation of theinvention, are not intended to limit the scope of the invention. Manymodifications, alternative constructions, and equivalents may beemployed without departing from the scope and spirit of the invention.

1. An aerosol injector, the injector comprising: a) a liquid tube, witha liquid tube orifice for ejecting a liquid to be atomized; b) apropellant cap comprising: i) an annular orifice, (1) the annularorifice disposed around an inner cylinder, (a) the inner cylinderpassing through the propellant cap, (b) the inner cylinder having aninterior, (2) the liquid tube disposed within the inner cylinderinterior; ii) an interior region flowing to the annular orifice; iii) agas line flowing a pressurized gas into the interior region, (1) the gasline having a gas line heater, (2) the gas line heater heating thepressurized gas to form a heated pressurized gas; iv) a heat transferregion disposed between the inner cylinder and the liquid tube; c) wherethe heated pressurized gas is ejected from the annular orificesurrounding the liquid ejected from the liquid tube orifice, atomizingand heating the liquid.
 2. The injector of claim 1 wherein: a) the heattransfer region is comprised of one or more materials with a thermalconductivity of less than or equal to$25{\frac{W}{m\;{^\circ}\mspace{14mu}{K.}}.}$
 3. The injector of claim 1wherein: a) the heat transfer region is comprised of one or morematerials with a thermal conductivity of less than or equal to$20{\frac{W}{{m\mspace{11mu}}^{{^\circ}}\mspace{14mu} K}.}$
 4. Theinjector of claim 3 wherein: a) the material is selected from the groupconsisting of: essentially stagnant air, epoxy, plastic, stainlesssteel, glass fibers, fluorocarbons and glass.
 5. The injector of claim 1wherein: a) the liquid is selected from the group comprising sealant,adhesive, coating, and paint.
 6. The injector of claim 5 wherein: a) theliquid tube has an essentially constant cross-sectional area in the heattransfer region.
 7. The injector of claim 1 wherein: a) the heattransfer region is comprised of one or more materials with a thermalconductivity of less than or equal to$10{\frac{W}{m\;{^\circ}\mspace{14mu}{K.}}.}$
 8. The injector of claim 1wherein: a) the heat transfer region is comprised of one or morematerials with a thermal conductivity of less than or equal to$5{\frac{W}{{m\mspace{11mu}}^{{^\circ}}\mspace{14mu} K}.}$
 9. Theinjector of claim 1 wherein: a) the heat transfer region contains anambient air flow; b) the ambient air flow is drawn by the heatedpressurized gas exiting the annular orifice; c) whereby the ambient airflow cools the liquid tube, and prevents boiling of the liquid.
 10. Theinjector of claim 1 further comprising: (a) an aerosol spray cone angleof less than 20°.
 11. The injector of claim 1 further comprising: (a) anaerosol spray cone angle of less than 15°.
 12. The injector of claim 1further comprising: (a) an aerosol spray cone angle of less than 10°.13. An aerosol injector, the injector comprising: a) a liquid tube, witha liquid tube orifice for spraying a liquid; b) a gas cap comprising: i)a gas nozzle, (1) the gas nozzle having an open cylindrical wall,forming an outer diameter of an annular tube, (2) a gas line feedinginto the gas nozzle, (3) a gas line heater for heating a pressurized gasin the gas line, forming a heated pressurized gas, (4) a venturi boredisposed within the gas nozzle and passing through the gas nozzle, (5)the venturi bore forming an inner diameter of the annular orifice; ii)the liquid tube passing through the venturi bore; iii) a venturi regiondisposed between the inner diameter of the annular orifice and theliquid tube; iv) where the pressurized gas introduced into the gas lineis heated by the gas line heater, and exits the annular orifice as theheated pressurized gas, drawing ambient air through the venturi region,thereby forming a venturi flow; c) whereby the venturi flow cools boththe inner annulus and the liquid tube, and thereby reduces heat transferfrom the heated pressurized gas to the liquid tube.